1. Field of the Invention
The present invention is related to an optical element for emitting an incident light beam in a desirable direction, an optical deflection element for emitting a plurality of light beams having different incidence angles or different wavelengths from each other in different directions, and an optical multiplexing element for optically multiplexing a plurality of light beams having different incidence angles in the same direction. Further, the present invention is related to a scanning apparatus with employment of such an optical deflection element.
2. Description of a Related Art
Conventionally, as an optical element or an optical deflection element, passive elements such as a prism, a diffraction grating, a concave lens and soon have been utilized. Further, very recently, as an optical deflection element, active elements such as a diffraction grating using an acoust-optic effect and a galvano scanner have been employed.
In such a diffraction grating using the acoust-optic effect, by propagating a compression wave (for instance, an ultrasonic wave) through a medium such as glass, a refractive index is changed periodically, so that a light beam is emitted in different directions. In a galvano scanner, by vibrating a mirror by using a resonant head, a light beam is emitted in different directions.
However, since the passive elements such as the prism, the diffraction grating, and the concave lens have a small deflection angle at which a light beam is emitted from the passive element, a long optical path is necessarily required so as to separate the incident light beam into a plurality of light beams corresponding to incidence angles or wavelengths. Therefore, in order that the light beams having different incidence angles or different wavelengths are deflected in a wide range, a dimension of such a passive element itself must be increased, and also the entire optical apparatus must be made large so as to secure the long optical path. On the other hand, in the active elements such as the diffraction grating using the acoust-optic effect and the galvano scanner, although light can be deflected in a wide range, cost of the active element itself is expensive, and also the active element owns a slow response to the input signals.
Very recently, specific crystal (namely, photonic crystal) having a different optical characteristic from that of the conventional optical crystal has been effectively developed. The photonic crystal owns a crystal structure in which, within a first medium, a second medium having a different refractive index from that of the first medium is arranged at an interval corresponding to a wavelength of light. The photonic crystal owns a refractive index distribution which is changed periodically, and shows such a phenomenon (namely, superprism effect) in which refraction directions of light beams having slightly different incidence angles or wavelengths from each other are largely changed. The optical characteristics shown by the photonic crystal are described in detail, for example, in “Superprism phenomenon in photonic crystals” written by H. Kosaka et al., Physical Review B Vol. 58, No. 16, Oct. 15, 1998, and in Japanese Laid-open Patent Application JP-A-2000-66002.
Currently, various optical elements with employment of such photonic crystal as manufacturing materials thereof have been proposed. For example, Japanese Laid-open Patent Application JP-A-2000-56146 discloses such a self-waveguide circuit provided with photonic crystal on a major portion of a substrate so as to propagate a light beam within the substrate in the self-waveguide manner to separate the propagated light beam into a desirable number of light beams. Also, Japanese Laid-open Patent Application JP-A-11-271541 discloses such a wavelength separating circuit having the photonic crystal interposed between two claddings as materials so as to separate a light beam in correspondence with wavelengths of the components.
However, those conventional techniques disclosed in the above-mentioned documents are directed to the optical separating operations of the light beams. Therefore, those conventional optical elements/circuits cannot be utilized as, for instance, an optical deflection element for deflecting a plurality of light beams having different incidence angles or different wavelengths in different directions. As described above, no one could succeed in developing of optical elements, optical deflection elements, nor optical multiplexing elements which employ the photonic crystal as manufacturing materials thereof.